The present invention relates to a disposable dispensing apparatus for delivering a powdered product nasally or orally. More specifically, but not exclusively, there is provided a single use dry powder medicament inhaler which can be used by persons who have not had medical training.
Such dispensing devices are well known in the art and are of particular use for the dispensing of drugs which can easily be absorbed through the nasal or pulmonary passages, especially for drugs which only need to be dispensed occasionally.
A dispensing device is known from U.S. Pat. No. 5,683,361 (incorporated herein by reference) which dispenses a single dosage of a powdery drug which is stored in a cylindrical storage chamber within the sealed main body of the device until dispensation of the drug is required. The chamber is located in an axially displaceable piston, which is mounted in the main body of the device between an end wall of the main body and a plunger for releasing the drug. The chamber is sealed with breakable membranes at either end of the cylinder which are, upon activation of the dispensing device, punctured by one or more perforating elements. An outlet duct is provided at the end of the main body remote from the plunger for dispensation of the drug to the user. The perforating element is provided at the end of the outlet duct nearest to the piston to puncture at least the outermost membrane of the drug chamber.
Both embodiments of the device described in U.S. Pat. No. 5,683,361 involve pressurization of the air inside the device prior to dispensation of the powdered medicament. When the plunger is pressed by the user into the main body of the device a pocket of air, which is trapped inside the main body of the device between the piston and the plunger, is compressed and the pressure inside the device increases. This increase in pressure causes the piston to move towards the outlet duct of the dispensing device, thereby causing the outermost membrane to be punctured by the perforating element. The remaining intact membrane is then punctured in one of two possible ways: by the penetrating element provided at the inner end of the outlet duct as the plunger, and therefore also the piston, is pushed further into the main body of the device, or by a second perforating element which is optionally provided at the inner end of the plunger.
A disadvantage with the devices described in U.S. Pat. No. 5,683,361 is that they do not always dispense the whole drug dose to the patient. As the outermost membrane is punctured, pieces of the perforated membrane are pushed into the chamber in the opposite direction to movement of the plunger and the desired drug flow path. This results in some of the powdered drug particles being trapped between pieces of the perforated membrane and the wall of the chamber as the drug is forced out of the dispensing device via the outlet duct. Furthermore, as the patient inhales, the pieces of the perforated membrane are drawn in the direction of the outlet duct and thereby interfere with the dispensing of the drug as the powder can no longer flow freely out of the drug chamber. In this way, the dose dispensed by the device is often incomplete, which can mean that the drug is not wholly effective.
Another single-use dispensing device is described in patent application GB 0025027.4 (incorporated herein by reference) which device comprises a bellows unit for pressurizing the interior of the device and for propelling the powdered drug out of the dispensing apparatus.
A single-use dispensing device needs to be simple and cheap to manufacture. The known devices described above require a sealed main body to enable the device to be pressurized.